Calculating a Butterfly valves torque (pls Help)

Actually no - that is not all the information that is required.

Usually these torque values can be obtained from the supplier/manufacturer.

Isn't a butterfly valve inherently balanced to a great extent?
The dynamics of the flow will exert some force on it, but I'd have thought the torque would be more to do with the bearings and seals than the pressure?

Not my field of expertise so feel free to shoot me down...
Del

That's right Del when it's partly open, but it takes some torque to overcome friction on initial opening. As the other guest said, best to ask manufacturer. Needn't necessarily be manufacturer of the valve in question, they're not likely to vary too much.

Cheers.........Codey

It also depends on if it is a regular or double/triple offset valve.

You right my friend.

Butterfly valve is inherently balanced, as in flow, and when we are trying to open or close the valve. half of the disc acts agains the flow, but other half gets compensatory assistance from the force generated by flow.

But is butterfly valve is eccentric shaft valve, this is not true. Torque required will be different while opening than while closing

My question is..............why would you want to use a butterfly valve............my preference would be a gate valve.

I know of ships the have ended up with serious flooding problems due to failure of butterfly valves in their ballast systems.

I cannot recall any warship that I served on ever having butterfly valves..........because of their inherent problems.........you cannot use those butterfly valves with rubber and plastic parts in any machinery space.............because of fire...........can only use all metal valves............same applies with ball valves.

If you wish to use butterfly valves make sure your plastic and/or rubber parts are correct for temperature, fluid purity (solids in suspension) and ph value, NOT only pressure.

Hello,

I had to calculate it some years ago and used AWWA C504 if I remember well.

The torque required is the maximum of two different calculations, by one side the required to overcome the seat friction and get it tight, and the other by calculating the hydrodynamic torque produced in the disc at different angles with flow direction plus the friction on upper/lower bearings. The ΔP usually have no effects on the calculation, is flow rate (medium speed) which produces hydrodynamic torque. Usually maximum hydrodynamic torque appears when the disc is about 30º from closed position.

Anyway you need some data from valve manufacturer. There is no valve torque/thrust calculation method (independent on the valve type) which doesn't need some valve data available just from manufacturer and usually aren't included in the standard drawings supplied.

Kind regards

Good luck with this one,

I can only say that when new, butterfly valves do not require to much force to open them. Flow control is easy enough they are more or less self balancing.

Wait until they age a bit, I had to remove the actuator from a 200mm valve a couple of weeks ago and pull on it with a twelve inch pipe grips just to break its grip in the seat.

That said, it had been a long time since the valve moved at all, so the rubber seat firmly grabbed.

Other valves of the same type and size only required a pneumatic actuator of double piston, spring back to center types, operating at 5 or 6 Bars. with a 200mm valve needing a 125mm (Piston) diameter actuator. It would follow that 400mm requires a 250mm diameter device to operate it.

Buy this book

1 Valve Handbook

by Philip L. Skousen

hi,

this calculation link will help for you to get your torque calculation

regards,

Samy

Hi,

this link will work for your torque calculation for butterfly valve.

http://www.abzvalve.com/PDF/Torque%20Calculation.pdf

regards,

Samy

Just ring the local friendly Valves Distributor.